Resolving chlorosilane mixtures



RESOLVING CHLOROSILANE MIXTURES No Drawing. Application October 29, 1952, Serial No. 317,592

Claims. (Cl. 260-448.2)

Patented June 26, 1956 to be a straight addition product of the silicon tetrachloride, which can be represented by the type formula SiCl4:2 amine. There are many of these tertiary amines which may be suitable for the purpose intended, and those which have been tested and found to form solid addition products with SiCli, or other chlorosilanes, include trimethylamine, triethylamine, and certain cyclic unsaturated amines, such as pyridine, 3-methyl pyridine, 4-(5-nonylpyridine, dipyridyl, phenazine and quinoline.

The following experiment will more specifically illustrate themethod proposed by this invention.

An azeotropic mixture of (CH2)3SiCl and SiCl4 was made up, and 150 grams of this mixture was treated with 2.6 moles of pyridine. The mixture was kept cool, at a The invention is concerned with the resolving of mixtemperature of about 0 C., until all of the SiClr (0.57 tures of chlorosilanes, and more particularly it relates mole) had reacted. The mobile slurry, containing preto a method for separating tetrachlorosilane, or other cipitated SiCl4..2C5H5N, was then distilled until the distilchlorosilanes, from mixtures thereof with organochlorolate was equivalent to 87% of the initial weight of silanes, such as trimethylchlorosilane. (CH3)3SiCl. All of the distilled portion had a density A common way of preparing methyl silicon chlorides of 0.86, which is identical with the reported values for consists in the reaction of methyl chloride with silicon, (CH3)3SiCl, and a chlorine analysis of a distilled fracusually in the presence of a copper catalyst. The prodtion showed 33.2% C1, compared with the calculated net of this reaction is mainly a mixture of methyl chloroamount in trimethyl chlorosilane of 32.7%. Thus the silanes and tetrachlorosilane. A clean separation of all recovered (CH3)3SiCl showed no evidence of appreciable components of this mixture is practically impossible by contamination with SiCli. ordinary fractional distillation, as trimethyl chlorosilane In resolving the product obtained from the reaction of and tetrachlorosilane have approximately the same boilmethyl chloride with silicon, the tertiary amines as deing point (about 575 C.). These compounds also form scribed will also provide a more ready separation between a constant boiling, or azeotropic, mixture, which contain-s other organosilanes and the halo-silanes. For example, the two chlorosilanes in approximately equimolecular a mixture of 0.283 mole of CH3SiCls With 0.079 mole of proportions, and which distills at about 54.5 C. under SiCli was treated with 0.786 mole of pyridine. The normal pressures. Since the trimethyl derivative, free methyl trichlorosilane was recovered by distillation at from associated silicon tetrachloride, has especial value 66 C. and the silicon tetrachloride, which boils at 58 C., and use commercially, particularly in the making of cerdid not come over, showing that it had been held back tain silicone polymer compositions, it is very desirable by reaction with the added pyridine. The precipitated to be able to recover the trimethyl chlorosilane in pure amine complex can be broken, subsequent to the sepand unadulterated form. aration, by treating it with anhydrous HCl.

While various means of accomplishing this end have, Other examples of the application of themethod of this heretofore, been proposed, which in general have followed invention are shown in the following table.

To Separate- From- Use- Forming Addition Compound Pyridine 81014.2 pyridine. S1014 Organo-silanes-. {3-Methy1Pyridine.... 81014.2 (S-Metbyl Pyridine). 4-Methyl Pyridine 81014.2 (4-Methy1 Pyridine). Pyridine SiHC1s.2 pyridine. SE01: do {3-MethylPyridine.... 811-101;.2 (ii-Methyl Pyridine). 4-Methyl Pyridine. SiHCh.2 (i-Methyl Pyridine). RsN' 2SlHO13.3R3N. Pyridine SiHiOhJ pyridine. Smack 3-Methyl Pyridine.... SiHiCh.2 (ii-Methyl Pyridine). 4-M ethyl Pyridine...- 811120112 (i-Methyl Pyridine). RgN" ZSiHzOhBRaN. Pyridine SizChB pyridine. snoi. .110 I snolta (3-Methyl Pyridine). 4-Methyl Pyridine. SizCh.3 (at-Methyl Pyridine).

R=CH: 0i C2H5. known methods of resolving other azeotropic mixtures, We claim: these have not been too satisfactory in commercial appli- 1. The method of separating inorganic chlorosilanes cation. it is, therefore, the object of this invention to taken from the group consisting of silicon chlorides and provide an improved method of resolving azeotropic mixhydrogen silicon chlorides from mixtures thereof with tures of trimethyl chlorosilane and silicon tetrachloride, alkylchlorosilanes, which comprises converting the inorand further to provide a means of effecting a more ready 6O ganic chlorosilanes to solid reaction products by addiand clean separation of silicon tetrachloride and other tion to said mixtures of a tertiary unsaturated-N-heterochlorosilanes from mixtures thereof with organo-chlorocyclic amine and distilling off the alkylchlorosilanes. silanes. 2. The method of separating inorganic chlorosilanes The invention is based upon title finding that certain tertaken from the group consisting of silicon chlorides and tiary amines will react with chlorosilanes, in particular 5 hydrogen silicon chlorides from mixtures thereof with silicon tetrachloride, to form solid reaction products, alkylchlorosilanes, which comprises converting the inwhereas these same amines will not combine with triorganic chlorosilanes to solid reaction products by addimethyl chlorosilane or the other organochlorosilanes. tion to said mixtures of an unsaturated heterocyclic amine Thus an azeotropic mixture of SiCl4 and (CHa)3SiCl can taken from the group consisting of pyridine, S-methyl be broken down by precipitation of the SiCl4, and the or- 7 pyridine, 4-methy1 pyridine, 4-(5-nonyl) pyridine, di-

ganochlorosilane can then readily be recovered by ordinary distillation. The solid formed in this reaction appears pyridyl, phenazine and quinoline and distilling oif the alkylchlorosilanes.

3. The method of separating inorganic chlorosilanes taken from the group consisting of silicon chlorides and hydrogen silicon chlorides from mixtures thereof with methylchlorosilanes, which. comprises converting the inorganic, chlorosilanes to solid reaction products by ad.- dition to said mixtures of an unsaturated heterocyclic aminetaken from the group consisting of pyridine, 3- methyl pyridine, 4-methyl pyridine, 4-(5-nonyl)pyridine, dipyridyl, phenazine and quinoline and distilling oh. the methylchlorosilanes.

4. Method of resolving an azeotropic mixture of trimethylchlorosilaneand silicon tetrachloride, which comprises converting the. silicon tetrachloride to a solid reaction product, by addition to said mixture of a cyclic, unsaturated, tertiary amine of the group consisting of pyridine, 3, and.4methyl pyridine, 4-(5-nonyl)pyridine, dipyridyl,.phenazine and quinoline and separating the trimethylchloro'silane. by distillation.

5. Methodof resolvingan azeotropic mixture. of trimetltylchlorosilane and. silicon. tetrachloride, which cornprises. converting. the. silicon tetrachloride to a solid reaction product, by addition of pyridine to said mixture, and separating the trimethylchlorosilane by distillation.

References Cited in the file of this patent UNITED STATES PATENTS 2,381,139 Sauer Aug. 7, 1945 2,388,575 Sauer'et a1. Nov. 6, 1945 2,449,815 Newkirk Sept. 21, 1948 2,485,366 Di Giorgio et aln Oct. 18, 1949 2,519,926 Patnode et a1 Aug. 22, 1950 2,567,724 Moody Sept. 11, 1951 2,580,473 Sowa Jan. 1, 1952 FOREIGN PATENTS 612,646 Great Britain Nov. 16, 1948 OTHER REFERENCES Etneleus; Nature, vol. 42. (1938), pages 996, 997. Trost: Canadian Journal of Chemistry, vol. 29 (1951), pages 107578. 

1. THE METHOD OF SEPARATING INORGANIC CHLOROSILANES TAKEN FROM THE GROUP CONSISTING OF SILICON CHLORIDES AND HYDROGEN SILICON CHLORIDES FROM MIXTURES THEREOF WITH ALKYLCHLOROSILANES, WHICH COMPRISES CONVERTING THE INORGANIC CHLOROSILANES TO SOLID REACTION PRODUCTS BY ADDITION TO SAID MIXTURES OF A TERTIARY UNSATURATED-N-HETEROCYCLIC AMINE AND DISTILLING OFF THE ALKYLCHLOROSILANES. 